ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Semiconductor Unilateral Switch - Thyristor

Updated on December 9, 2017
Ayyanalee profile image

I'm a student of Electronic Engineering, also an been blogging for 3 years I can write well about my subject on basics and also about a blog


Semiconductor unilateral switch also abbreviated as SUS, it is a two terminal, four-layer device. It will start conduction when the specific forward voltage is applied to its terminals. As we know it is four-layered, there are three junctions when the forward voltage is applied across its terminal two junctions J1 and J3 get forward biased and middle junction which is J2 gets reversed bias. J2 junction holds the current until applied voltage across its terminals reaches specific forward breakdown voltages of the device since the applied voltage across terminal reaches the forward break over voltage J2 will be broken and the device will start conducting.

Figure 1.1 - Construction and Schematic Symbol
Figure 1.1 - Construction and Schematic Symbol


It is very easy to understand the construction of two transistor equivalent circuit of SUS. Transistor equivalent circuit is given in figure 1.2 (b). Let's assume four-layers are split in such way that it looks like two transistors i.e. PNP and NPN as shown in figure 1.2 (a). Both transistors are connected in such way that the base of Q1 is connected with the collector of Q2 and base of Q2 is connected to the collector of the Q1.

Figure 1.2 - Transistor Equivalent
Figure 1.2 - Transistor Equivalent

Working Operation

To understand the working operation, Assume a transistor equivalent circuit of a SUS - thyristor connected with variable DC power supply in forwardly biased manner. As shown in figure 1.3. When VS is increased from zero VAK will also increase, SUS block conduction until VAK reaches to the VBR (Foward Biased Breakover voltage). When VAK reached to VBR there will be enough leakage current from Q1 to turn on Q2. This leakage current will cause Q2 into the saturation state, hence conduction through the device will be stared.

Figure 1.3 - Response of SUS
Figure 1.3 - Response of SUS

The voltage VAK will be decreased because it behaves like a short circuit which provides the least resistive path to current. The forward current through the saturated SUS can be found as:


    0 of 8192 characters used
    Post Comment

    No comments yet.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)